Distinct SOX9 single-molecule dynamics characterize adult differentiation and fetal-like reprogrammed states in...

Transcription factors (TFs) mediate gene expression changes during differentiation and development. However, how TF biophysical properties and abundance dynamically regulate specific cell state transitions remains poorly understood. Using automated live-cell single-molecule tracking (SMT) in intestinal organoid models, we revealed an expression-level-independent decrease in the fraction of immobile sex-determining region Y box 9 (SOX9) molecules during differentiation from ∼48% to ∼38%, largely dependent on DNA binding. Strikingly, long-term SOX9 overexpression caused organoids to transition from budding to spheroid morphology accompanied by increased proliferation and a loss in gene expression signatures for intestinal identity and function. In this fetal-like reprogrammed state, a larger fraction of partially self-interacting SOX9 molecules (∼61%) binds to DNA. Our results suggest context-dependent SOX9 single-molecule dynamics during adult intestinal differentiation and fetal-like reversion in consequence to long-term SOX9 overexpression. Our work underpins the power of our automated live-cell SMT framework to generate testable hypotheses toward unraveling molecular mechanisms underlying tissue-level phenotypes.